The present invention generally relates to surface-acoustic-wave devices and more particularly to a surface-acoustic-wave device for flip-chip mounting.
Surface-acoustic-wave devices hereinafter designated as SAW devices are used extensively in various electronic apparatuses having a high-frequency circuit, including portable telephone sets, wireless telephone sets, and various radio sets. By using a surface-acoustic-wave device, it becomes possible to reduce the weight and size of these electronic apparatuses.
On the other hand, the demand for size and weight reduction is still continuing in electronic apparatuses and hence in the SAW devices used therein. In the case of SAW devices, the size reduction has to be achieved so as to avoid deterioration of attenuation characteristic outside the pass-band.
FIG.1 shows an equivalent circuit diagram of a SAW filter of a related art having a ladder-type construction, while FIG.2 shows the actual construction of the SAW filter of FIG.1 in a cross-sectional view.
Referring to FIG.1, the ladder-type SAW filter includes resonators 13 and 14 connected in series and interposed between an input terminal 11 and an output terminal 12, and there are provided parallel resonators 15, 16 and 17 respectively shunting a signal path between the input terminal 11 and the SAW filter 13, a signal path between the SAW filters 13 and 14, and a signal path between the SAW filter 14 and the output terminal 12, to the ground. These resonators 13-17 are formed on a common piezoelectric substrate 10 of a LiTaO3 or LiNbO3 single crystal.
FIG.2 shows the piezoelectric substrate 10 in the state that the piezoelectric substrate 10 is mounted on a filter package 20.
Referring to FIG.2, the filter package 20 includes a bottom part 21A covered by a conductor film 21a and a side wall part 21B, wherein the bottom part 21A and the side wall part 21B form together a depression 21C. Thus, the piezoelectric substrate 10 is accommodated in the depression 21C in such a manner that the piezoelectric substrate 10 is mounted on the conductor film 21a covering the bottom part 21A in a face-up state by way of an adhesive layer 21b. Thus, an electrode pattern corresponding to the equivalent circuit diagram of FIG.1 is formed on the top principal surface of the piezoelectric substrate 10. Further, wiring patterns 21c and 21d are formed on the top surface of the side wall part 21B, and the electrode pattern on the substrate 10 is connected to the wiring patterns 21c and 21d via respective bonding wires 22A and 22B.
It should be noted that the SAW device 20 of FIG.2 further includes a frame part 21D on the top surface of the side wall part 21B so as to expose the wiring patterns 21c and 21d, and a metal cap 23 is provided on the frame part 21D. The metal cap 23 is connected to the ground pads 21e and 21f provided on the bottom surface of the bottom part 21A via respective ground patterns 22e and 22f formed on the frame part 21D. Further, the wiring patterns 21c and 21d on the side wall part 21B are connected also electrically to corresponding electrodes that are provided on the bottom surface of the bottom part 21A.
In the filter package 20 of FIG.2, the bonding wires 22A and 22B are used for electrical connection between the SAW device on the piezoelectric substrate 10 and the wiring patterns 21c and 21d. In order to accommodate such bonding wires, the SAW device of FIG.2 has used the frame part 21D, while such a construction inevitably increases the height of the SAW package 20 and thus contradicts with the requirement of size reduction of SAW devices.
Accordingly, it is a general object of the present invention to provide a novel and useful SAW device wherein the foregoing problems are eliminated.
Another and more specific object of the present invention is to provide a SAW filter device having a compact size and simultaneously an excellent spurious suppression performance outside a pass-band.
Another object of the present invention is to provide a surface-acoustic-wave device, comprising:
a piezoelectric substrate;
an electrode pattern provided on a principal surface of said piezoelectric substrate, said electrode pattern forming a ladder-type surface-acoustic-wave filter; and
a package body accommodating therein said piezoelectric substrate,
said package body comprising: a bottom part carrying said piezoelectric substrate in a face-down state; and a side wall part laterally surrounding said piezoelectric substrate on said bottom part,
said bottom part and said side wall part forming together a depression accommodating therein said piezoelectric substrate,
said bottom part carrying a wiring pattern for electrical connection with said electrode pattern,
said wiring pattern including a first ground pattern and a second ground pattern in a mutually separated relationship on said bottom part, said first ground pattern and said second ground pattern being connected electrically with each other.
Another object of the present invention is to provide a surface-acoustic-wave device, comprising:
a package body having a mounting surface;
a piezoelectric substrate mounted on said mounting surface in a face-down state;
a first electrode pattern provided on a principal surface of said piezoelectric substrate facing said mounting surface in said face-down state of said piezoelectric substrate, said first electrode pattern forming a ladder-type filter; and
a second electrode pattern provided on said principal surface of said piezoelectric substrate, said second electrode pattern forming a double-mode-type filter;
each of said first and second electrode patterns including a plurality of ground electrodes formed on said principal surface,
said mounting surface carrying a first ground pattern making a contact commonly with said plurality of ground electrodes of said first electrode pattern, said mounting surface further carrying a plurality of mutually separated second ground patterns each making an electrical contact with a corresponding one of said plurality of ground electrodes of said second electrode pattern.
According to the present invention, the space needed in the SAW device of the related art at the top part of the package body for accommodating the bonding wires is eliminated, and the size of the SAW device is reduced successfully. By forming the first ground pattern on the package body as a part of the electrode pattern of the ladder-type filter in such a manner that the first ground pattern makes a contact with the ground electrode of an input/output shunting resonator, and by forming the second ground pattern on the package body so as to make a contact with the ground electrode of the intermediate shunting resonator shunting an intermediate signal path of the ladder-type SAW filter, and further by connecting the first ground pattern and the second ground pattern electrically, suppression of spurious components outside a pass-band of the SAW filter is improved substantially. The degree of suppression of the spurious components is improved further by interposing an inductance between the first and second ground patterns and by optimizing the value of the inductance.
By forming the ground electrodes in the form of stacking of a plurality of bumps, or by forming the wiring patterns on the mounting surface in the form of stacking of a plurality of conductor patterns, the problem of short circuit caused between the electrode pattern on the piezoelectric substrate and the ground pattern on the mounting surface is successfully eliminated.
The present invention is applicable also to a SAW device in which a plurality of electrode patterns including the ladder-type electrode pattern is formed on the principal surface of the piezoelectric substrate. The SAW device includes the one in which an electrode pattern corresponding to a double-mode-type filter is provided on the principal surface of the piezoelectric substrate in addition to the ladder-type electrode pattern.
Other objects and further features of the present invention will become apparent from the following detailed description when read in conjunction with the attached drawings.